This invention relates to the stacking of folded paper sheet signatures ("signatures") and more particularly to an apparatus and method for automatically and reliably stacking signatures delivered from web finishing equipment for a printing press.
Machines capable of stacking signatures have a wide range of uses in many industries. One such use is to collect paper that has been folded by an automatic folding machine. One known folding apparatus can fold freshly printed signatures in half or thirds at speeds at, or even in excess of, the line speed of a printing press. A stacker operating in conjunction with such a paper folder must be both fast and reliable. Specifically, a stacker used with such high speed on-line web finishing equipment for a printing press such as the aforementioned insert folder must be capable of stacking a flow of mutually spaced apart signatures at speeds of up to 60,000 signatures per hour. Of course, it is also of great commercial value to have a stacker which can operate reliably and at high speed in conjunction with off-line web finishing equipment.
A number of attempts have been made to produce a stacker which can reliably stack signatures at high speeds. One such stacker includes a belt which carries signatures in a horizontally oriented position towards a vertical stop wall. After the signatures strike the stop wall, they fall straight down into a stacking compartment in front of the wall. The stacker has not been very successful when operated at high speeds because signatures do not fall into the compartment in an orderly fashion. As a result, jams are likely to occur forcing the shut down of the printing process.
Another known stacker will take signatures which are part of an ordinary shingled stream of signatures which are traveling in a horizontal path and capture the shingle stream between a drum roll and a belt. The combination of the drum roll and the belt carries the signatures through a 180 degree turn. When the signatures come out of the 180 degree turn, they strike a stop wall which defines a stack. Each successive signature which is carried around a drum roll inserts itself beneath the preceding signature. As each signature is inserted beneath its preceding signature, the remainder of the stack is forced in an upward fashion in order to accomodate the following signatures. While this stacker may operate well at high speeds, the duration of such high speed operation is severely limited by restraints placed on the stack size. As the signatures build up, the stack above the entering signature becomes heavier. Eventually, the weight of the stack reaches a point where entering signatures can no longer force themselves under the stack. As a result, the entering signatures jam and the line must eventually be shut down to clear the jam.
In addition to being stacked at line speed, the signatures must be subject to a minimum of handling since it is still possible that, if there is printed material on the signatures, the ink on the signatures may be wet and subject to being smeared. It is also important that the stacker create an ordered stack and handle and stack any reasonably sized signatures. Also, changes in the size of the stack as more signatures are processed should not slow down the stacking, nor should it have any effect on the quality of the stack.
It is therefore a principal object of the present invention to provide an apparatus and method for stacking signatures received from a web finishing apparatus, particularly an automatic folder, at line speed or higher.
It is a further object of the present invention to provide a signature stacking apparatus which is capable of stacking signatures fresh off a printing press without excessive smearing of ink on the paper.
Another object of the present invention is to provide an apparatus and method for stacking signatures which produce an orderly stack.
Yet another object of the present invention is to provide an apparatus and method for stacking signatures which will stack signatures of variable sizes with a high degree of reliability.